The fortunes of potential U.S. allies among Syrian opposition groups "are ebbing fast" as hardline Salafist groups and the Nusra Front — al-Qaida’s Syrian affiliate — "go on the offensive," according to the cable network.

During the past month, already embattled moderate groups have lost ground in the critical northern provinces of Aleppo and Idlib, dealing a blow to the administration’s efforts to "stand up" moderates so they can take on the Islamic State (ISIS), which currently occupies much of Iraq and Syria.

While the United States has announced a plan to train 5,000 fighters over the next year at a cost of $500 million, the training has not begun, and some of the most likely recipients of U.S. aid "are now in retreat or on the verge of extinction," CNN reported.

These groups, it adds, suffer from low morale and "are caught between a rock and a hard place, pilloried by radical factions for taking Western weapons but failing to get enough of them (or quickly enough) to become serious players."

According to Kimberly Kagan, president of the Institute for the Study of War, "the forces that the U.S. has nominally been backing have suffered losses" at the hands of the Islamic State, the Nusra Front, and the Assad regime.

If current trends continue, it means that "the moderate opposition remains marginal and incapable of shaping the battlefield in any material way," Kagan said.

Worse still are indications that ISIS and the Nusra Front have reached a truce, enabling them to consolidate their gains and fight other opponents inside Syria.

During the past month, ISIS has reportedly overwhelmed forces of the Syrian Revolutionaries' Front and Harakat Hazm in Idlib, groups supported by Washington and Saudi Arabia.

The Revolutionaries' Front "had been seen as a potential U.S. ally" after helping to expel ISIS fighters from part of northwestern Syria in January. Numerous Harakat Hazm fighters reportedly defected to the Nusra Front.

Most territory in Syria is said to be run by the "big three": ISIS, the Nusra Front and its allies, and the Assad regime.

"The Americans have painted themselves into a corner, left to work only with so-called moderates, who at this point have mostly been kidnapped, killed, exiled or absorbed into Islamist factions," Kristen Gillespie, founder of a website called Syria Direct, told CNN.

That, says CNN, "fits the al-Assad regime's game plan. Kill off the mainstream groups and leave the West with a stark choice: Bashar al-Assad or ISIS and other jihadist groups turning Syria into an Islamic state."